I´m quite fat, 85 kg. My biggest kite right now is a 12m and I can't afford to buy a new one now.

Question is if I should go somewhere else where it's more windy... After a quick research on google I found this island "Isla Mujeres, Mexico" which at least is windy right now judging by windguru... perhaps a coincident? Tulum looks not even kiteable when I check on windguru.

Isla Mujeres is close to cancun which is handy, but perhaps also damn expensive compared to other places?

Tommorrow will be 21-25 Knots because a nice northern system coming. It will be perfect in Isla Blanca (Cancún) for the 9. But I never kited on isla mujeres. I only heard about Cozumel.
In winter we get mostly SE 12-17 knots, Maybe better for Your 12. Occassionally we get N NE with stronger winds for 9m.

Many people also stay at the Kite school in isla blanca calles Ikarus, you can Google it quite reasonable.